Artificial line



R. S. HOYT.

ARTIFICIAL LINE.

APPLICATION FILED JULY 9.19m

Patented Dec 5, 1922.

INVENTOR 12,5217 4;

0 a4 02 as 04 as as a? :26 0:240

a 1 ATTORNEY Patented Dec. 5, 1922.

UNITED, STATES PATENTOFFICE.

RAY S. HOYT, OF BROOKLYN, NEW YORK, ASSIGNOR TO AMERICAN TELEPHONE ANDTELEGRAPH COMPANY, A CORPORATIONOF NEW YORK.

ARTIFICIAL LINE.

' Application filed July 9, 1919. Serial No. 309,633.

17 '0 all whom it may concern: I

Be it known that I, BAY S. HOYT, residing at Brooklyn, in the county ofKings and State of New York, have invented certain Improvements inArtificial Lines, of which the following is a specification.

My invention relates to an artificial line for simulating-the impedanceof a periodically loaded line over a preassigned range of frequencies,as, for example, the range of frequencies necessary for the telephonictransmission of speech. In the following specification I disclose anembodiment of my inventionconsisting of an artificial line designed tosimulate a geographically extended loaded transmission line. Theaccompanying drawings relate to this example of my invention, but itwill be understood that the invention is defined in the appended claims.

The basic form of the artificial line of my present disclosure, thoughpossessing prop erties closely analogous to those of the basic form ofthe artificial line of my previous disclosure, covered by U. S. PatentNo. 3,167,693, dated January 11, 1916, is nevertheless entirely distincttherefrom and independent thereof. Not only is it entirely different inform, but it is also different in function, in that it simulates theline impedance at an entirely different point within the loaded line,namely at a certain point in a loading coil, which point is hereindesignated a basic position, instead of at a point in a loading section.

Of course, in actual practice, geographical lines do not generallyterminate at what I have designated a basic position. The actualtermination of a line may, in fact, be a full loading section(distancebetween load coils) or. any fractional part thereof, de-

pending upon geographical factors, er it may be a full'loading coil orany fractional part thereof according as convenience dictates. However,like the basic artificial. line disclosed in my aforesaid patent, thebasic artificial line of my present invention admits of being extendedso as to simulate the impedance of a loaded line terminating at anyother post-ion than the basicposition. For a certain range of lineterminations my present artificial line is simpler and cheaper than myaforesaid previous artificial line, while for a certain other range theaforesaid previous artificial line is the simpler and the cheaper; buton the whole the two possess about equal utility.

The above-mentioned analogy between the basic form of my presentinvention and the basic term of my aforesaid previous invention consistsin the fact that the mathematical expression for the admittance of mypresent basic. artificialline is of the same form as the mathematicalexpression for the impedance of my aforesaid previous basic artificialline; while there is a similar correspondence between the mathematicalexpressions for the admittance and the impedance of the actual loadedlines simulated by thesetwo basic artificial lines. Stated morespecifically, my present basic artificial line simulates the admittanceof a loaded line that terminates with a certain fractional loading coil,with the same precision as my aforesaid previous basic artificial linesimulates the impedance of a loaded line that terminates with thecorresponding frac tional section. As will appear in detail below,extensive use is here made of this mathematical analogy in the deductionand presentation'of the properties of the artificial line constitutingmy present invention. However, this is done merely for the sake ofsimplicity and to save labor; it not being essential, as of course theproperties of the network constituting my present invention could bededuced and presented from either an impedanceviewpoint or an admittanceviewpoint quite independently of my previous invention.

In the accompanying drawings, Figure 1 illustrates diagrammatically abasic form of artificial line arranged in accordance with my presentinvention; Fig. 2 shows a modification of the invention providing whatmay conveniently be termed a consolidated form; 3 shows anothermodification of the invention, providing a still simpler though somewhatless precise form; Fig. d presents a series of curves show ng the,simulative precision of my invention, as embodied in Fig. 1; Fig. 5presents a series of curves showing the applicability of the invention;and Fig. 6 illustrates a supplementary structure for taking into accountthe effect of line wire resistance and load coilresistance.

Preliminary to the development of the general theory underlying thisinvention it may be remarked that the term characteristic mid-loadimpedance is commonly used to denote the characteristic impedance of aperiodically loaded line which begins with a half-coil; that is, a coilwhose inductance is half the inductance of each ofthe succeeding coils.In what follows, it will be convement'to employ, in addition, the moregeneral term characteristic w-load impedance to denote thecharacteristic impedance of a loaded line which begins at 7 load;thatis, with acoil whose inductance bears the ratio as to the inductanceof each of the succeeding coils.

The general theory underlying this invention will now be developed. Suchtheory canbe based more simply and more conveniently on a generalformula for the characteristic' w-loa'd admittance of a periodicallyloaded line than on the corresponding for-mulafor its reciprocal, thecharacteristic w-load impedance. For any fixed frequency and initialtermination, said admittance, as is well known, depends mainly on theline capacity and on the load coil inductance; but also,to aslightextent, on the distributed line-induotance. This small effect producedby the distributed line induct'ance will not be neglected, but will betaken into accountin the same manner as has already been fully set forthin my previous Patent No; 1,167 ,693, wherein it is shown that, asregards characteristic midload impedance (and hence as regardscharacteristic mid-load admittance), a periodically loaded line havingdistributed line in ductance in addition to its lumped load coilinductance is simulated to a high degree of precision by a, certainperiodically loaded line having no distributed line inductance buthaving an inductance L per load coil and acapacity $00 per loadingsection where s is'the spacing 'of the load coils, that is, the distancebetween adjacent coils, and L and C are approximately equal to thecorresponding constants of the actual loaded line,

that is,to its inductance L per load coil and to its capacity C per unitlength, respectively; said constants being related in accordance withequations (15) and (16) of my aforesaid Patent No. 1,167 ,693.

With the effect produced by the distributed inductance thus takenaccount of, the general theory underlying this invention may be based onthe relatively simple formula forthe characteristic w-load admittance ofthe aforesaid L C equivalent loaded line having no distributedinductance. Such formula, which will next be de veloped, will be based,in turn, on the formula for the characteristic mid-load impedwhere c'designates the imaginary operator 1 and p denotes 211- times thefrequency Equation (1) can be readily proved from the fact thati L /Z isthe impedance of a half-load coil and ipmL is the impedance of an m-loadcoil, so that the difference ipazL -pL /2 is the amount by which theimpedance of an w-load coil exceeds the impedance ofa half-load coil andhence is the amount by which thecharacteristic impedanceH of a loadedline which begins at m-load exceeds thecharacteristic impedance H of aloaded line which begins at mid-load. But from equation (14) of myaforesaid Patent No. 1,167,693 the value of H is, very closely,

where o= 1 w m =flfc.. -(3 and 7', denotes the critical frequency,

f -a=1/7rvm 4 so-named because at this pyarticular frequency asudden'change occurs in the line properties (propagation constant andimpedance) and in its immediate neighborhood those properties varyrapidly with frequency. Efiicient transmission is inherentlyobtainablefrom (3)-and (4c) and denoting the quantity /sC /L byT we findthat Denoting by Z the characteristic m-l'oad ad mittance," which is thereciprocal of the characteristic zv-load from I that T /1 w, +tT w (12m) where D and Q are respectively the real andthe imaginary parts ofthe right-hand side of equation (6).; D thus being the characteristicav-load conductance of the L G loaded line, and the characteristic'oc-load susceptance thereof.

Equations and (5) express the characteristic impedance of a loaded linehaving no resistance in the line wires and in the loading coils. Theeffect of the actual resistance in modifying the characteristicimpedancehas been fully set forth in my previous Patent N0.1,167,693,wherein such effect is shown to be small; and wherein, moreover, it isshown how to take account of impedance H we find .saidjeflect in thosecases for which said ef fect is not entirely negligible. As pointed outlater herein, the effect of the actual resistance of the line wires andthe coils in modifying the characteristic admittance can be similarlytaken account of, when desired;

but further discussion of this feature will be deferred for the present,as the effect in question is not only small and comparativelyunimportant, but is also of such a nature as to admit of beingrepresented independently (by an added term) and taken account ofindependently (by an added branch).

Returning now to equation (6) for the characteristic zv-load admittance,and comparing same with equation (19) for the characteristic ac-sectionimpedance as given in my aforesaid Patent No. 1,167 ,693, it will' beobserved that these two equations are ex- .actly alike (although, to besure, the c0nstants w and T do not have the same meanings in both), Inother words, the characteristic m-load admittance and the characteristic:Jfi-SQCtlOIl impedance are exactly the same functions of. theindependent variable w (although the parameters w and T involved donot'have the same meanings in the two expressions. This identity in theform of the two expressions (which constitutes the math ematical analogymentioned above) enables extensive use to be made here of themathematical developmentsgiven in my aforesaid Patent No. 1,167 ,693, aswill appear more in detail below. h

The circuit arrangement which simulates the admittance expressed byformula 6) (for a particular value of a: specified later herein) isrepresented by Fig. 1. It is in the nature of a basic structure, and isthe part termed, above, the basic artificial line. consisting of thecapacity C, in series with The portion.

the inductance L simulates the susceptance component Q, of Z as given byequations (6) and Referring to said equations it will be seen that theimaginary or susceptance component may be written But the admittance ofa capacity C in series with an inductance L is well known to beexpressible as i 0C, l 3 32 Comparison of this expression with theright-hand side of equation (8) shows that they are identical providedthat C, and L be given the following values C,:(1/2w)s0 9 It is thusseen that the (],L portion of the basic structure simulates thesusceptance component of the admittance of the L loaded line providedthat Q, and L are pro portioned in accordance with equations (9) and(10). Of course physical limitations restrict the choice of w to thosevalues for which U and L are positive, but that means only that 00cannot exceed 1/2, while it can have any value from O to 1/2.

Equations (6) and (7) show that the con ductance component of thecharacteristic admittance of the L C loaded line is given by D 1 490(100w; A plot herewith (Fig. 5) of the coe'lficient of T in this equationshows that said conductance component D has a drooping characteristicfor values of a: less than 0.17, and finally becomes zero at 20 :1. Nowa conductance element, in series with the combination consisting of aninductance element and a capacity element in parallel with each other,will have a similar conductance charac'teristic provided that theinductance condenser portion is anti-resonant in the nei hborhood of10, 1. The admittance of a conductance C in series with the combinationconsisting of an inductance L and l condenser C in parallel with eachother, is

well known to be are therefore the conductance and suscep- A, H's, 12 1tance components respectively of the admit- From analogy with therelations set" forth in e nations and (3a) of my aforesaid atent No.1,167,693, it is now clear that the conductance component of thecharacteristic m-load admittance of the L C loaded line can be simulatedover the range w,,:() to 10 :1, by the conductance component A of anetwork made up of a conductance element G in series with thecombination consisting of an inductance L and a capacity C in arallelwith each other, by assigning the ollowing values:

a fii n moo 01: (2.023) sCo (16) L .1oe9 L, l 17 Equations (15), (16),(17) thus constitute the designformulae 1n accordance with which Iproportion the G O L portion of the artificial line.

Fig. {l serves to show the high degree of precision with which theconductance component A approximates the conductance component D of theline admittance. In said Fig. 4, the curve 1 is a plot of theconductance component of the admittance of the L C loaded line having aninitial fractional coil of (Hall while the curve 2 is a plot of theconductance component A of the admittance of my artificial line; theabscissm being the values of w The susceptance component B must be.neutralized since it does not usefully simulate any component of theline admittance. By analogy with the relations disclosed in my aforesaidPatent No. 1,167 ,693, it may be seen that this neutralization can beaccomplished very closely by shunting the Gr C L- portion of thestructure with a capacity of C in series with an inductance L providedthat c o.120 8c0 i 19 If, in equa curve 4 is a plot of the susceptanceof the G L portion of Fig.1, when a: is assigned;

- the particular value 0.14. If 41::014, its" value hereinbeforeassigned to it, equations (9) and (10) become v a O3: (0L3600)i8C L v L='(()i.3344)L;' L l (22')' If, their, the elements of" the str am showninFig. 1 are proportioned in" accord '80 ance with equations 15 (222inclusivglthje structure simulates very close y over thdentire range offrequenciesnecessary for tele phonic transmission of s, ech, theadifii'fl' tance of the L C lo'aded line havin an ini tialfractionalcoil equal 'to 0.14 This is illustrated tin-Fig 4, the cohd ucj tance simulation is shown by curves 1 Mid"? already referred to; wllile the-su'seeptmcejsimulation is shown by curves '5" and 6, which areplots of the susceptance component of the L C loaded line and of thsus'oeptancbfi component of the structureshown in Fig." 1, respectively.P

It will be noted that the basic structurede signed in accord'ancewith'the desi forinu he (15) (22') inclusive, simulates t tantra-' teristicadmittance of the L Cglfoadedli'll'ek having a particular initialfractional coil possessing an inductance equal t0*0-.'14 D 10i) sincethe simulation is-most precise for this" particular fractional value ofthe initial-coil asL In general, ofcourse, the line may have any coil asits initial 'coil (usually, however,

either a whole coil or a half coil); or it may I begin with a wholesection or a fractional" section instead of with a wholecoil or afractional coil. It therefore becomes neces sar to supplement the basicstructure-to thef enc that it may simulate the admittance of a linehaving an initial coil or an initial section of any value. Thism'ay bemom plished, for example, by adding to the arti ,f ficial line anextension so that the extended artificial line shall be equivalent 'toaglinella having whatever initial termination is contemplated. It willbe understood thatsuch extension may be proportioned in accordance withL, and G If it is desired to talre into account th'e-re' slightly lessprecision, the resistance eifect can berepresented by merely a"condenser C,

and an inductance L (Fig- 6) placed' inf series with the network, whichcondenser and inductance may be proportioned in accord-" ance with therelation set forth in my pro-* vious Patent No. 1,167,694 just as thoughthe line were uniformly loaded instead of periodically loaded, thisassumption being pero,=(0.4sa)8o, (2a

L,: 0.265 L, 2a

A still simpler form, represented by Fig. 3, can be gotten from thebasic structure represented by Fig. 1, though at a somewhat greatersacrifice of simulative precision, by omitting altogether the C Lportion and the 0 L portion, and at the same time adopting a somewhatdifferent proportioning for the C L portion; and this constitutesanother simplified embodiment of my invention. The reason for. adoptingsomewhat different proportioning of this form is the fact that theconductance component of the characteristic w-load admittance can besimulated by a mere constant conductance most accurately when m is equalto about 0.2, since then the said conductance component is most nearlyindependent of w as shown by Fig. 5. The best value for Gr is stillapproximately that expressed by formula (15); and the best values for Gand L are those expressed by formulae (9) and (10) after insertingtherein the particular value chosen for 0a (approximately 02). Thusequations (15), (9),

and (10) constitute the design-formulae for the simplified networkrepresented by Fig. 3.

This invention, as in the case of the inventions disclosed in myaforementioned Patent No. 1,167,693, finds its application where theimpedance of a loaded line is to be simulated; as for instance, forbalancing purposes in systems involving two two-way telephone repeaters;and in other transmission systems.

illustrative example worked out in my pre vious Patent No. 1,167,693;that is, an aerial line consisting of two parallel #8 B. W. G. copperwires, loaded at intervals of 8 miles (8:8), but beginning withahalf-coil (instead of with a. 0.11-section, as inthe abovementionedillustration); the distributed in ductance, J, per mile of line is0.0034 henries; the capacity, C, per mile is 0.0092 10' farads; thetotal resistance per mile including load coil resistance is 5 ohms; andthe induction per load coil is 0.2 10 henries.

Then, as already computed in my Patent No. 1,167,698, L and C have thevalues: L,:O.258 henries, (J :0.O088 l0* farads.

The values of the elements constituting the basic structure (Fig. 1) forsimulating the impedance of the L G loaded line when beginning with afractional coil of inductance 0.140(0258 henries are then, by aid of thefore oing computations together with equations (15)(22), found to be asfollows: F. :1/G :1910 ohms; C :0.144 10- farads; L :0.0276 henries; C:0.00853 l0' farads; 11 20330 henries; C ::0.0256 10 farads; 11 200863henries.

To simulate the characteristic mid-load impedance, as required, thisbasic structure must evidently be extended by means of a seriesinductance having a value equal to (0.5O.14)L that is, 0.0093 henries.

If particularly high simulative precision is desired, to take account ofthe effect produced by the wire resistance and the loadcoil resistanceof the given loaded line, this may be accomplished by connecting inseries the supplementary part shown in Fig. 6, consisting of aninductance 14 2000090 hen- \'-ies,and acapacity G :6.77 10 farads.

If theconsolidated form of network shown in Fig. 2 is desired, theconstants C and L are determined by equations (23) and (2e)(3,:002544060 fara'ds, and L :O.0684c henries.

If the still simpler form of network shown in Fig. 3 is desired, and ifapproximate simulation is required over as wide a range as possiblerather than more precise simulation over a narrower range, then a; wouldbe chosen as 0.2; whence, by (9) and (10), the constants (l and L, are:(3 :0.021-3X1O farads, and L :0.138henries. The value of R II/G is, by(15), 1%,:1910 ohms.

Although I have shown and described herein only a few forms ofartificial lines embodying my invention, it is readily understood thatother changes and modifications may be made therein within the scope ofthe following claims withoutdeparting from the spirit and scope of myinvention. Furthermore, although I have shown these forms of artificiallines as designed to simulate a geograpically extended loadedtransmission line, it will readily be understood that according to theprinciple of my present invention, artificial linesmay be made osimulate other examples of loaded lines.

WVhatI claim is:

1. In an artificial line a network 'comprising a plurality ofparallelpaths, one of said paths comprising a resistance element and theother inductance and capacity reactant-e elements connected infserieswith each other, the values of said elements being such that theimpedance of, the network simulates that of a loaded line beginning at apoint in a loading coil. v

2. An artificial line simulating the characteristic admittance of loadedline, said artificial line including means having an admittance Whoseconductance component simulates the conductance of theloaded linebeginning ata point Within a loading coil,

.means for neutralizing the susceptance omponen of the, admittance of Sfi m d mean 3. :An at i ic al ine imula g h c amp .tcristic admittance.of a loaded line, said artifici ll ne c mpri ing a -Pai of p l e P 113: 9 Y nc udingts issepi an e devic s simulating the" suscepta icecomponent of the dmittanceof the loaded line, the other ineludingconductance and susceptance elements providing admittance having a con.ductance component simulating the conductance of' the loaded linebeginning at a point Within a loading coil,cand means for neutralizingthe susceptance component of the admittance produced by said conductanceand susceptance elements, whereby the joint admittance of saidconductance and .susceptance elementsand of saidneutralia ng means hasnosusceptance component.

4. In a'nartificialline simulatin'gl he char- .acteri tico dmittance ofallowed n ginning ,at 'a-point ithin a loadin coil the combination ofmeans for s ml at g the susceptance component of said admittance, meanscomposed'of conductance and susceptance elements providing an admittanchavin ga conductance component simulatingthe conductance component ofthe a it a ce o sai T oa c line b g nning at a point withinaloa dingcoil and means Iior neutralizing the susceptance component oftheadmittance produced by said conductance and susceptance elements 5.artificialline'sirnulating,the char-- acteristic I-adm ttance of aloaded l ne said lart i ifils ns in ludi g th c mbi ti n of .aresi wjice eleinentin se ies t a indu tame element an a, cond nse onne e 111ra l W t a h o h r, vs wmbinat hav a ad itt nc ho e onduc a component smulates the conductance componentoftheladmittanoe of the loaded line,and means for neutralizing the susceptance component of the admittanceofsaid'combination.

6. An artificial linesimulatingthe characteristic admittance of aloadedline', said artificial linecoinprisinga path containing aresistance, an lnductance and a. condenser simulating the conductanceof' the .iloaded line, and asecond path in parallel to the fir an lw tenmgan i tenseia a com denser, 'inlilatin th gs'c'seept c 2 loaded'line;said resistances, inductances and condensers having values depending onathe load coil inductance, the distance between consecutive load coils,the capacity andinducta-nce of said loaded line, and the distributedcharacter of said line inductance.

7. An artificial line simulating-the characteristic impedance of aloadediline, said artificiallinehaving a portion-containing a resistanceelement in series With inductance and capacity elements connected inparallel With each other anrl portion .in. parallel ,with saidotherportion andconsistin'g an inductance element in series with a capacityelement; said resistance, inductance fjandfcapacity elements havingvalues dependingon the load coil inductance, the distance betweenconsecutive loadcoils, the caipacity and inductance of said line betweenloads and the distributed character of said line inductance.-

tw en loads a th A, distrib ted, tqha eqcrb said line inductance. a I'9- fi i im s m la n h characteristic impedance of a loadeg-line saidartificial line comprising. a portion consi ing of an inductance coil inseries ,yvith' a condenser, said portion simulatingitheefiect of theline between loads and; load fcoiljre sistance, a portion consistinq ofa resi stance elementiin serieswith an 1 uctance coiland condenserconnected in parallel, and' a portionconsisting of an inductance coil inseries with a; condenser, the first of said portions 1 c nnected inse ew th fill d W1 la m nti n ope i ns a s a ed'fw 9 each ethe i p a l l rlat qns ipza i t widths o ld res st nc 'iafil icta i la d -ecit'ylements being l eta m' n iby'ihe 19a n an e and si -anc ,jtherdist n e htween consecutiveload coils; the res tant e, capacity and inductance ofsaid lineand the distributed character of saidline inductance.

10. .An artificial line simulatin' r the I acteristic impedance ofloadef line, said artificial line comprising a' portion consistingor aninductance "coil in series with a condenser, said portion s1mulatingiheif ect oftherline andloa'd coil resistance; asecond portion consisting.of a; resistancejlelementjin series withan inductance coiland ba condenpa alle Ii t a e c ,oflwpat gt ether s me ah init atin lie inductancecoil in series with a condenser, the last three of said four portions ofsaid artificial line being connected in parallel with each other and thefirst portion thereof being connected in series with the said threeportions, and the values of said resistance, inductance and capacityelements being determined by the load coil inductance and resistance,the distance between the consecutive load coils, the resistance,capacity and inductance of said line and the distributed character ofsaid line inductance.

11. In an artificial line simulating the characteristic admittance of aline, a sub combination simulating the conductance component of saidadmittance and comprising a portion consisting of a resistance elementin series with an inductance coil and a condenser connected in parallelwith each other, and a portion consisting of an inductance coil and acondenser in series; said portions being connected in parallel with eachother, and said resistance, capacity and inductance elements havingvalues depending on the load coil inductance, the distance betweenconsecutive load coils, the capacity and inductance of said line betweenloads and the distributed character of said line inductance.

12. A network for simulating the impedance of a circuit comprising shuntcapacity and lumped series inductances placed at sub stantially equalcapacity intervals, said net work comprising a plurality of parallelpaths, impedance elements in said paths, the values of said elementsbeing such that the conductance of one of said paths is substantiallyequal to the conductance component oi the admittance of the circuitbeginning with a fractional inductance coil and the susceptance ofanother of said paths is substantially equal to the susceptancecomponent of the said admittance.

13. A network for simulating the impedance of a circuit comprising shuntcapacity and lumped series inductances placed at substantially equalcapacity intervals, said network comprising a plurality of parallel.paths, one of said paths comprising inductance and capacity elements inseries with each other approximately to simulate the susceptancecomponent 01" the line as a whole and another of said paths comprising aresistance element in series with an inductance and capacity elementconnected in parallel with each other,

14-. A network for simulating the impedance of a circuit comprisingshunt capacity and lumped series inductances placed at substantiallyequal capacity intervals, said net work comprising a plurality ofparallel. paths, two of said paths comprising inductance and capacityelements in series with each other one of said two paths approximatelysimulating the susceptance component of the line as a whole and anotherof said paths comprising a resistance element in series with aninductance and a capacity element connected in parallel with each other.

In testimony whereof, I have signed my name to this specification this30 day of June RAY S. HOYT.

